1. Field of Disclosure
The disclosure relates to a pipeline analog-to-digital converter (ADC), and more specifically to selective compression of an analog input signal of the data converter to improve input noise performance and dynamic input range.
2. Related Art
Data converters are frequently used in a mixed-signal electronic system that includes an analog signal domain and a digital signal domain. The analog signal domain primarily operates upon an analog input signal while the digital signal domain primarily operates upon a digital output signal. A mechanism is required to transport signals from the analog signal domain to the digital signal domain in the mixed-signal electronic system.
Commonly, a conventional analog-to-digital converter (ADC) is used to convert an analog input signal from the analog signal domain to a digital output signal for the digital signal domain. The conventional ADC includes multiple quantization levels that are used to assign the analog input signal to a combination of bits, referred to as a codeword. The conventional ADC selects one of the quantization levels that is closest to the analog input signal and provides the combination of bits that corresponds to this selected quantization level as the digital output signal.
A ratio between a minimum quantization level and a maximum quantization level may be referred to as a dynamic input range of the conventional ADC. Often times, the dynamic input range of the conventional ADC is determined such that a maximum value of the analog input signal is less than or equal to the maximum quantization level and a minimum value of the analog input signal is greater than or equal to the minimum quantization level. When the conventional ADC is used in a wideband communication system that combines various communication signals to form communication signals that have high peak to root mean square (rms) ratios, the peaks of these communication signals determine the minimum quantization level and the maximum quantization level. In most situations, the analog input signal is significantly less than the peaks of these communication signals. As a result only a narrow range of the available dynamic input range is utilized by the conventional ADC which reduces its accuracy. Some of the outermost quantization levels, those furthest from a mean value of the analog input signal, are rarely, if ever, utilized by the conventional ADC in the wideband communication system. As an alternate, the dynamic input range of the conventional ADC can be narrowed to only cover those values of the analog input signal which are commonly observed. In this situation, when the analog input signal falls below the minimum quantization level and/or rises above the maximum quantization level, respectively, the conventional ADC saturates or clips. As a result, the digital output signal no longer accurately represents the analog input signal when clipping occurs.
The present disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.